bug#54043: Simple regexp bug [contains spoiler for today's wordle]

[Matthew Wilcox]

I noticed this one while doing:

$ grep sha[^s]e five-letter-words
share

which doesn't fit with:

$ grep sha.e five-letter-words
shade
shake
shale
shame
shape
share
shave

A reproducer is easy:

$ echo shame |grep sha[^s]e
(no output)

Almost any change to the regex & input will make it work, even rot-13
of both.  For example:

$ echo shamel |grep sha[^s]e
(no output, still fails)
$ echo shamel |grep sha[^s]el
shamel
$ echo sshame |grep ssha[^s]e
sshame
$ echo funzr |grep fun[^f]r
funzr

$ grep --version
grep (GNU grep) 3.7
Copyright (C) 2021 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and others; see
<https://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.

This is Debian amd64, grep package version 3.7-1.